Computing devices, such as notebook computers, personal data assistants (PDAs), mobile communication devices, portable entertainment devices (such as handheld video game devices, multimedia players, and the like) and set-top-boxes (such as digital cable boxes, digital video disc (DVD) players, and the like) have user interface devices, which are also known as human interface devices (HID), that facilitate interaction between the user and the computing device. One type of user interface device that has become more common is a touch-sensor device that operates by way of capacitance sensing. A touch-sensor device usually is in the form of a touch-sensor pad, a touch-sensor slider, or touch-sensor buttons, and includes an array of one or more capacitive sense elements. The capacitance detected by a capacitance sensor changes as a function of the proximity of a conductive object to the touch sensor. The conductive object can be, for example, a stylus or a user's finger.
One type of capacitance sensing device includes multiple touch sense electrodes arranged in rows and columns and forming an array of intersections. At each intersection of the electrodes in the X and Y axes (i.e., a location where the approximately orthogonal electrodes cross over, but do not connect with, one another), a mutual capacitance is formed between the electrodes thus forming a matrix of capacitive sense elements. This mutual capacitance is measured by a processing system and a change in capacitance (e.g., due to the proximity or movement of a conductive object) can be detected. In a touch-sensor device, a change in capacitance of each sense element in the X and Y axes of the touch sense array can be measured by a variety of methods. Regardless of the method, usually an electrical signal representative of the capacitance of the capacitive sense elements is measured and processed by a processing device, which in turn produces electrical or optical signals representative of the position of one or more conductive objects in relation to the touch-sensor pad in the X and Y axes. A touch-sensor strip, slider, or button may operate on the same or another capacitance-sensing principle.
The processing system may have a number of receive channels, each of which can receive the electrical signal associated with one or more different sense elements. Certain processing systems may have a limited number of these receive channels, however, which limits the number of measurements that can be performed at a same time. For example, if the processing system has four receive channels, then only four sense elements can be measured in parallel to detect a change in capacitance. For large touch-sensor devices that contain a high number of sense elements in the array, sequentially scanning the elements in these groups of a limited size (e.g., four at a time) may be prohibitively time consuming.